There is known a sheet binding apparatus that binds an edge portion of a sheet bundle with an adhesive tape up to now. The sheet binding apparatus includes a bundle forming section and a tape attaching section. The bundle forming section stacks a plurality of sheets to forma sheet bundle. The bundle forming section forms a side portion of the sheet bundle in a step shape in order to secure a surface area during tape attachment. The tape attaching section attaches the adhesive tape to an edge portion of the sheet bundle to bind the sheet bundle. The tape attaching section includes a tape holding section that holds the adhesive tape. The tape attaching section includes a first roller and a second roller opposed to each other in the sheet bundle thickness direction. The adhesive tape is peeled from the tape holding section by inserting the sheet bundle, which is shifted in the step shape, toward the adhesive tape held by the tape holding section. Thereafter, the sheet bundle is rushed inbetween the first roller and the second roller together with the adhesive tape to stuck the adhesive tape to the edge portion of the sheet bundle.
However, the following problem is likely to occur depending on the magnitude of a pressing force on the sheet bundle inbetween the first roller and the second roller (between the rollers). For example, if the pressing force on the sheet bundle between the rollers is too small, the adhesive tape cannot be sufficiently adhered to the edge portion of the sheet bundle. On the other hand, for example, if the pressing force on the sheet bundle between the rollers is too large, the sheet bundle cannot be rushed into between the first roller and the second roller.